Antenna switching device



June 25, I946. R. B. HOFFMAN 2,402,625

ANTENNA SWITCHING DEVICE Filed Nov. 12, 1941 FIG. 1.

ANTENNA 77?.4/V5M/77ER arcs/V52 INVERTER L13 DELAY IMPULSE flack/[V6c/Rc U/T GENERATOR CIRCUIT FIG. 2. FIG. 3.

HVVENTOR.

ATTORNEY.

Patented June 25, 1946 2,402,625 ANTENNA swrronmo DEVICE Ross B.Hoffman, East Orange, NHL, assignor to Federal Telephone and RadioCorporation, a corporation of Delaware Application November 12, 1941,Serial No. 418,671

12 Claims.

1 This invention relates to improvements in antenna coupling devices,and in particular to such devices as applied to enemy aircraftidentiflca tion by friendly aircraft or by antiaircraft stations. Atypical system to which the invention is applicable has been disclosedin the copending application of H. G. Busignies, Serial No. 417,151,filed October 30, 194i, and entitled "Aircraft identifier.

Systems have been devised, especially in the police radio field forutilizing one antenna for both transmitting and receiving. Suchsimultaneous operation can be attained when both transmitting andreceiving equipment is operating on slightly different frequencies; and,if only one frequency be used, switch-over from transmitter to receivermay be accomplished by ordinary relayapparatus.

In connection with the use of impulse-energyoperated systems forobstacle identification purposes on the ground or in aircraft, it may bedesirable to use only one antenna for transmission and reception on thesame frequency with changeover as rapid as a few microseconds, or even afraction of a microsecond. It is wellknown that impulse systems of thenature referred to involve the transmission of relatively large amountsof power and detection of relatively weak signals. As a result, previousswitchover methods and systems may not be satisfactory in impulse sytemsof this character.

Accordingly, it is an object of the invention to provide improved'meansfor enabling concurrent transmission and reception on a common antenna.Another object is to provide improved means for permitting alternatetransmission and reception of radiant energy of substantially the samecarrier frequency on a single antenna. A further object is to provideimproved switching means. It is a more specific object to provideimproved means permitting the use of 4a single'antenna for transmissionof impulse energy and detection of a reflection thereof.

Other objects and various further features of novelty and invention willhereinafter be pointed out or will occur to those skilled in the artfrom a reading of the fOllOWing specification in conjunction with thedrawing included herewith. In said drawing Fig. 1 is a schematic blockdiagram illustrating an embodiment of the invention; and

Figs. 2 and 3 show alternative preferred forms of portions of theembodiment shown in Fig. 1.

As above indicated, in systems employing transmission and reception ofimpulse energy characterized by the same carrier frequency,cer-

. 2 deemed desirable for this purpose to employ permanently coupledtransmission lines between the antenna and both the transmitter andreceiver, and to make use of additional circuit elements alternately toblock each of these trans-- mission lines.

It is known that a resonating section of transmission line, A wavelength long, short-circuited at one end, and coupled to anothertransmission line may introduce substantial voltages into the Apreferred embodiment of the invention as thus applied is shown in Fig. 1where a single antenna i0 is employed for transmission and reception.Antenna l0 may be directly coupled as shown to a transmitter H by asuitable transmission line l2 and'to a receiver l3 by line [4. In orderalternately to block transmission lines l2 and i4, short-circuitedcoupled sections I5 and tain difiiculties may arise in the use ofpresent I6, respectively are provided coupled to each of these lines.

As indicated above it is expressly contemplated that my invention willbe applicable to concurrent transmission and reception of impulseenergy, re:

ception being operative during intervals between transmission ofindividual impulses, Due to the extremely rapid rate of switch-overrequired,

however, mechanical systems for varying the resonance, and henceblocking eflect, of coupled sections l5 and it are deemed inappropriate.

Accordingly, in accordance with the invention I tion IS in a detunedstate,-whereby substantially no blocking of received energy results. Avery short instant before the transmission of an impulse,.tube circuitI8 is appropriately energized" as to present such reactance to coupledsection l6 that the section 'will resonate and thus prevent anytransmitted energy being dissipated in line H. This condition ofresonance is preferably maintained for the duration oi. the transmittedimpulse and a very short instant thereafter in order to be absolutelysure of blocking reception of impulses as they-are transmitted. 'Sinceit is desired to make line I: conductivewhile line I4 is not, tubecircuit 11 for coupled section I5 is 3 preferable operative in a senseinverse to circuit l8, as will be clear.

The circuit of Fig. 1 shows schematically how the desired relation ofblocking and passing effects of coupled sections l5 and I 6 may beobtained. In accordance with known practice an impulse generator l9 maybe employed in the generation of impulses to be transmitted and at thesame time for energizing an appropriate blocking circuit 20 to assurethat the receiver is inoperative as individual impulses are beingtransmitted. As indicated, blocking circuit 20 may supply a blockingsignal of slightly greater duration than that of the transmittedimpulses. Suitable means for generating such a signal has been disclosedin the copending application of E. Labin, Ser. No. 386,282, filed April1, 1941, and entitled "Pulse modulation system. In the form shown, inorder to assure that transmitted impulses may fall within theabove-mentioned blocking interval, appropriate time delay means 2| maybe included in the line energizing transmitter ll.

In accordance with a feature of the invention I employ energy suppliedby blocking circuit 20 to control the alternate resonant and nonresonantconditions of coupled sections l5 and I6. As mentioned, the output'ofblocking circuit 20 is a series of impulses of slightly greater durationthan the transmitted impulses. In the form shown, these blockingimpulses may be applied directly to tube circuit l8, and means (notshown) may be provided to control or adjust the magnitude of theseimpulses to assure resonance in section 16 while such impulses are beingsupplied. In order to energize tube-circuit l1 appropriately, aninverter circuit 22 of known construction may be employed to feedcircuit I1 with blocking-energy inverse to that which is being suppliedcircuit [8. Thus, coupled section l5 may be maintained normally in acondition of resonance; that is, during intervals between transmissionof impulses, to prevent received energy from being dissipated intransmission line I 2, as will be clear.

In Fig. 2 I show a preferred embodiment of a possible tube circuit forperforming the functions above mentioned in connection with circuits l1and I8. In this embodiment a short-circuited quarter-wave length section23, which may correspond to section l5 or ii in Fig. 1, may be renderedalternately resonant and non-resonant by corresponding alternatesubstantial application and removal, as the case may be, of a shuntimpedance supplied as the output of tube 24. This function of tube 24 isobtained in accordance with blocking signal energy, which may besupplied in the manner above indicated, to the input 25 of the device.In a well-known manner, blocking, or resonance exciting, energy isapplied over a coupling condenser 26 and across a resistance, which inthe form shown includes a resistor 21 and a portion of a bias-controlpotentiometer 28.

Turning in more detail to a consideration of tube connections to coupledsection 23, output of tube 24, which in the form shown includes acathode, control grid, screen grid. and anode elements, may be appliedto the section at points 3 the voltages at these points being 180 out ofphase. Both supply lines include blocking condensers 3|, 32, and one ofthese lines further includes a resistor 33. Resistor 33 is preferably ofsuch a magnitude that the value of the RC network formed by resistor 33and the grid-cathode capacitance of tube 24 will-displace the phase ofthe radio-frequency grid voltage substantially with respect to that atoint 29. Inasmuch as the plate current of tube 24 is in phase with thevoltage applied to the control grid, this current leads the voltage atpoint 30, because voltages at points 29, 30 are out of phase, as will berecalled. It thus becomes clear that radio frequency plate current fedinto section 23' through blocking condenser 32 may produce an effectiveshunt capacity across the section, since voltage and current, as aboveindicated, are substantially 90 out of phase.

This effective shunt capacity may varywith the amplification or outputof the tube. Accordingly, appropriate adjustment, say of grid bias bymeans of potentiometer 28, may control the magnitude of shunt reactanceacross points 29, 30 to a desired degree, depending on the ma nitude ofblocking signal applied at input 25. As desired, radio frequency chokes34. 35 may be provided in the input and output circuits of tube 24 toisolate grid and plate supply respectively, and a screen grid voltagemay then be supplied over a resistor 36.

The unit shown in Fig. 2 would preferably normally be adjusted so thatcoupled section 23 would be detuned when no signal is supplied to input25. Upon application of the signal of fixed amplitude, the resultantreactance across the section would be such as to resonate the section,thus preventing flow of current in the transmission line to which thesection is coupled, as will be clear.

It is further clear that in an alternative embodiment the physicallength of section 23 may be so designed that the large effective shuntcapacity due to the circuit of Fig. 2 when a si nal is applied willdetune rather than resonate the section, and so that the normalefl'ective shunt reactance ofiered by the circuit when no signal isapplied will permit section 23 to resonate. Thus, when a blockingimpulse is impressed at input 25, section 23 may be detuned to permitpassage of energy along the line to which it is coupled; and when theblocking impulse is removed, a blocking effect results on the line.Thus, the identical blocking impulse, which served in thefirst-discussed case to produce a blocking action on the line to whichthe section was coupled, may also serve in this alternative embodimentto pass energy along a line; and, during the interval no blocking signalis applied, the former section may be detuned to pass energy, whereasthe latter may resonate and block. It would, therefore, be clearlypossible in an alternative embodiment of the circuit of Fig. l to employa coupled-section circuit of the former nature coupled say to line l4,and one of the latter nature coupled to line l2. In such case, theblocking signal obtained fromv circuit 20 could be supplied directly totube circuits i7 and I8, and there would be no need for inverter 22.

In Fig. 3 I show a further preferred embodiment of possible circuits I!or IS. The circuit employed makes use of the property of a A; wavelengthline to present an impedance varying in phase at one end of the linewhen a shunt resistance at the other end is varied.

In the form shown a wave-length line 31 may be connected to a coupledsection 23'- between points 29', 30" in a manner which may be similar tocorresponding connections shown in Fig. 2. Line 31 is shown terminatedby a shunt inductance 38 and by the respective outputs of ably soselected as to have a value permitting resonance with the internalcapacities of tubes 39 and 40, for a purpose that will readily beunderstood.

As in the case of Fig, 2 the gain of tubes 39 and 40 may be controlledby appropriate adjustment of a bias-control potentiometer 29'. It willbe clear that as bias of tubes 39 and 40 isthus varied, these tubes maybe made to operate within a range from cut-off to saturation, and thatconcurrently the eil'ective shunt impedance offered by the platecircuits of these tubes may vary from a resistive value of Q/wC as amaximum to a value approximately equal to l l m39 m40 as a minimum,where Gm39 and Gmm are the mutual conductance values of tubes 39 and 49,re-' spectively. It is considered that such a, variation will besufilcient to produce 1. large enough phase variation at the 29', 39'end of line 31 to tune and detune coupled section 23' completely.

The efiective shunt impedance presented by the plates of tubes 39 and 40may be varied by varying the voltage applied to the grids, as introducedacross resistor 21' nd a portion of potentiometer 29'; and the exactpoint of operation, as aboveindicated, may be determined by adjustmentof potentiometer 29'. I prefer to .make such adjustment so that platecurrent Will flow in tubes 39 and 40 when no signal is applied. Underthis condition section 23' would be non-resonant or detuned, and noblocking effect would be obtained in the transmission line to whichsection 23' is coupled. Since section 23' is thus detuned, substantiallyno current will be induced therein from the line to which it is coupled,and consequently no loss will ensue, due to the low resistanceintroduced by tubes 39 and 40 being coupled to line 31.

When, thereafter, a blocking signal characterized by a negative impulseis applied, tubes 39 and 60 will be cut oil, thus permitting section 23'to resonate with the reactance presented by the A; wave-length lineterminated by the parallel shunt combination of inductance 33 and theinternal capacities of tubes 39 and 49. Under this condition no flow ofcurrent will take place in the transmission line to which section 23' iscoupled, but a high circulating current will be present in the circuitcomprising section 23', line 31, and the tuned circuit made up ofinductance 6 and the tube capacities.

It will be recalled from the discussionof Fig. 2 that the physicallength of section 23 may be designed to resonate when the efiect of thetube circuit across points 29, 30 is substantially open circuit and todetune when the eifective shunt capacity is large. An analogousvariation may be made in the circuit of Fig. 3 by also appropriatelydesigning the length of the section (23'). In the thus modified form ofFig. 3 section 23' could be made to resonate normally, that is, while noblocking signal is applied to the input, and to detune when a negativeblocking impulse is applied. In such case, then, it would be possible touse say the first-described embodiment of Fig. 3 to block and open lineI4, and the latter to perform the inverse function with regard to line12, as will be clear. It thus appears that coupled sections l5 and I6could be made alternately to operate in inverse senses upon applicationof the same negative blocking signals simultaneously to both tubecircuits |'I,. l8. Naturally, of

course in this proposal, as-in the case of the corresponding proposalinconnection with Fig. 2, there would be no need for inverter 22.

Although I have described the embodiment shown in Fig. 3 as operativeupon application of a negative blocking impulse, it is clear that it mayalso operate upon application of positive impulses. In this case, tubes39, 40 would normally be biassed below cut-oif, and application ofblocking impulses of correct magnitude could be made either to resonateor detune section 23', depending upon the designed physical lengththereof in view of the foregoing discussion.

I have purposely omitted any reference in this disclosure as to whatpoint along the section the tube circuit should be inserted, inasmuch asthe particular connection point is considered relatively unimportant. Iprefer, however, to employ some point along the sectiongenerallyintermediate the open and shorted ends. The reason for suchpreference is clear. 1 capacity were inserted near the shorted end thevoltage shunted would be relatively low and pracsion systems." On theother hand, at resonance,

voltages across the open end are a maximum and may be so great as toproduce deleteriousor undesirable effects on the tube circuits.Accordingly, as indicated, some intermediate position is preferred.

Although I have described my invention in particular detail inconnection with transmission and reception on a common antenna, it isclear that the antenna is merely illustrative, for it may be consideredrepresentative, for example, of a transmission line or other network inconjunction with which concurrent transmission and reception aredesired. It is also clear that many modifications. additions, andomissions may be made within the scope of the invention.

What I claim is:

1. A radio system including impulse transmitter means, antenna means,receiver means responsive to reflections of impulse energy transmittedby said transmitter means, a firstv transmission line connecting saidtransmitter means to said antenna means, a second transmission lineconnecting said receiver means to said .an-

tenna means, impedance varying means'spaced from each of saidtransmission lines and respectively coupled thereto and means controlledby said impulse transmitter means alternately rendering saidimpedancevarying means effective ontheir respective transmission linesto render said first and then said second transmission lines ineffectiveto pass such impulse energy.

2..A radio system including transmitter means transmitting periodicallyrecurrent impulse ener y, antenna means. receiver means responsive Ifthe efiective shunt 7 alternately rendering said first and saidsecondmentioned connecting means ineffective to pass such impulse energyin accordance with said pefi'odic recurrence.

3. An impulse energy transmission and reception system including animpulse transmitter, a receiver, an antenna, connecting means connectingsaid transmitter and said receiver to said antenna, and control meansrendering said connecting means inefl'ective alternately to connect saidtransmitter and said receiver to said antenna, said control meansincluding a relatively short section of transmission line coupled tosaid connecting m ans and short-circuited at one end of said section,and means controlled by said transmitter periodically varying theeffective shunt reactance between points on each side of said section. v

4. An impulse energy system according to claim 3, in which saidconnecting means includes a transmission line coupling said transmitterand said antenna, and a transmission line connectin said receiver andsaid antenna, and in which said control means includes one said sectioncoupled to said first transmission line and another said section coupledto said second transmission line.

5. An impulse energy system according to claim 3, in which saidconnecting means include a transmission line coupling said transmitterand said, antenna, and a transmission line connecting said receiver andsaid antenna, and in which said control means includes one said sectioncoupled to said first transmission line and another said section coupledto said second transmission line, and wherein said periodically varyingmeans is connected between points on each side of each said section andperiodically varies the effective shunt reactance between said points onsaid one section in a sense inverse to such periodic variation betweensaid points on said other section.

6. The method of varying the resonant condition of a /4 wave-lengthtransmission line having one end short-circuited, which comprisesconnecting one end of a wave-length line between points on each side ofsaid transmission line and varying a resistance connected across theother end of said A; wave-length line.

7. The method of transmitting impulse ene y and receiving reflectionsthereof on a single antenna connected to an impulse transmitter and areceiver, there being'a section of transmission line inductively coupledto the line connecting the transmitter and antenna-and another suchsection inductively coupled to the line connecting the,antenna andreceiver, which method comprises resonating the section of transmissionline inductively coupled to the' line connecting the receiver andantenna during transmission of impulse energy, and resonating thesection of transmission line inductively coupled to the line connectingthe transmitter and antenna during intervals between said transmissionof impulse energy.

8. The method of transmitting impulse energy and receiving reflectionsthereof on a Single antenna connected to an impulse transmitter and areceiver, there being a section of transmission line inductively coupledto the line connecting the transmitter and antenna and anothersuchsection inductively coupled to the line connecting the antenna andreceiver, which method comprises resonating the section of transmissionline inductively coupled to the line connecting the receiver and antennaduring transmission of im- 8 pulse energy while detuning the section oftransmission line inductively coupled to the line connecting thetransmitter and antenna; and resonating said second-mentioned sectionwhile detiming said first-mentioned section during intervals betweensaid transmission of impulse energy.

9. In a system for controllingener y flow alon a transmission line, ashort circuited quarter wave-length section inductively coupled to saidline, means including vacuum tube controlmeans connected across saidsection and forming a variable efi'ective shunt reactance across saidsection for alternately tuning and detuning said section in accordancewith signals applied to said vacuum tube control means, said controlmeans including a vacuum tube having a cathode, a control grid, and ananode, means connecting said grid to one side or said section, and meansconnecting said anode to the other side of said section, saidfirst-mentioned and said second-mentioned connecting means eachincluding means eifecting substantially a relative phase displacementbetween current in each said connecting means.

10. In a system for controlling energy flow along a transmission line, ashort-circuited quarter wave-length section inductively coupled to saidline, means including vacuum tube control means connected across saidsection and forming a variable effective shunt reactance across saidsection for alternately tuning and detuning said section in accordancewith signals applied to said vacuum tube control means, said controlmeans including a pair of vacuum tubes, each of said vacuum tubesincluding a cathode, a control grid, and an anode, a wave-length linehaving one end connected across said section and each side of the otherend connected to the anode of one of said vacuum tubes, means connectingthe grids of said tubes, and an impedance bridging said other end orsaid 3 8 wavelength line, said impedance beingsuch as to form withinternal impedances of said tubes a resonant circuit.

11. In a system for controlling radio frequency energy flow along atransmission line, a shortcircuited line section inductively coupled tosaid transmission line, and control mean connected across said sectionand forming a variably reactive shunt impedance across said-section fortuning and detuning said section in accordance with variation of saidcontrol means, said control means including a A; wave-length line havingone end connected across said section, and means producing a variableresistance effect across the other end oi. said wave-length line.

12. A radio system including transmitter means for transmission at agiven carrier frequency, antenna means, receiver means responsive tosaid given carrier frequency, a first transmission line connecting saidtransmitter vmeans to said antenna means, a second transmission lineconnecting said receiver means to said ant a means, impedance varyingmeans spaced m each of said transmission lines and respecti ely coupledthereto, and means responsive to energy from said transmitter foralternately rendering said impedance varying means effective on theirrespective transmission lines to render said first and the said secondtransmission lines ineffective to pass energy of said given carrierfrequency.

- ROSS B. HOFFMAN.

